The present invention relates generally to a transmitter and, more particularly, to a transceiver having the same in a radio-frequency identification (RFID) system.
RFID technology is prevalent and applied nowadays in various industries such as electronic payment, security and stock inventorying, etc. FIG. 1 shows a structure of a conventional reader 1 in an RFID system. The reader 1 may include a directional coupler 10 having four ports (101, 102, 103 and 104), an antenna 11, a transmitter portion 12 and a receiver portion 13. The transmitter portion 12 includes an oscillator 121, a surface acoustic wave (SAW) device 122, an amplifier 123, a first diode 124 and a forward power leveling controller 125. The receiver portion 13 includes a second diode 131, an amplifier 132 and a comparator 133.
A signal from the transmitter portion 12 may be sent to the antenna 11 through the directional coupler 10. However, the four-port directional coupler 10 may largely attenuate signals from the transmitter portion 12 and therefore the attenuated signals transmitted from the antenna 11 may not have sufficient power to activate an electronic tag (not shown).
Still referring to FIG. 1, the first diode 124 and the forward power leveling controller 125 form a feedback path to monitor output power and maintain an amplitude of transmitted RF signal at a desired level. Complex feedback mechanisms must be developed to help the first diode 124 and the forward power leveling controller 125 controlling the output power. Moreover, it may take lots of efforts to solve problems such as stability when designing the feedback mechanism.
It may therefore desirable to have a cost efficient device with a simplified circuit.